One of the major advances in communications in recent years has been the increased use of optical systems for carrying very large quantities of information with low distortion and at low cost over great distances. Optical systems are also promising for such purposes as computing because of the inherently high speeds at which they can be operated. For these reasons, considerable work has been done to develop convenient techniques for operating on transmitted information-carrying light to produce various device functions. Devices known variously as hybrid optical integrated circuits, photonics modules, or hybrid optical packages have been proposed for controlling light using waveguide patterns similar to the electronic circuit patterns used in electronic integrated circuits.
The paper, "Glass Waveguides on Silicon for Hybrid Optical Packaging," C. H. Henry et al., Journal of Lightwave Technology, Vol. 7, No. 10, October 1989, pp. 1530-1539 describes a method using successive layers of glass over a silicon substrate to define optical waveguides. One layer of glass having a relatively high refractive index is the core layer and is surrounded by glass having a lower index of refraction. During operation, the light is confined in the core glass because of the lower refractive index of surrounding glass and, as a consequence, the configuration of the core layer defines the path of the light. Such waveguide configurations, sometimes referred to as optical circuits, can be fabricated with precision by masking and etching the core layer. The Henry et al. paper describes how various passive devices such as couplers and polarization splitters can be made from optical waveguides fabricated in this manner. A similar approach for defining optical circuits is described in the patent of Kawachi et al., U.S. Pat. No. 4,557,099, granted Jun. 14, 1988.
Any hybrid optical packaging approach of the type described above will typically require a number of forty-five degree mirrors, known in the art as turning mirrors, for coupling light between optical waveguides of the device and external devices such as lasers and photodetectors. The Kawachi et al. patent uses separately formed glass elements having forty-five degree mirror surfaces for providing this function.
The value of hybrid optical packaging is that it is amenable to mass production using known techniques of chemical vapor deposition, photolithography, and other techniques described in the Henry et al. paper. It would be desirable to be able to include turning mirrors in such packaged devices without incurring significant additional costs.